Contact angle θ in general is discussed in U.S. Pat. Nos. 6,303,225 and 6,461,731, the disclosures of which are hereby incorporated herein by reference. In certain instances, high contact angles are desired, while in other instances low contact angles are desired. The desired contact angle depends upon the situation in which an intended product is to be used.
It is known in the art to coat a glass substrate with a layer of titanium oxide (e.g., TiO2, or other stoichiometry). A layer of titanium oxide, if provided as the outermost layer on a glass substrate, can achieve a rather low contact angle θ with a sessile drop of water after lengthy exposure to ultraviolet (UV) radiation and water.
However, titanium oxide layers are problematic with respect to durability. For example, the scratch resistance of a titanium oxide layer is not that much better than that of glass. As a result, coated articles with an exposed layer of titanium oxide are highly susceptible to damage (e.g., scratching) during transport and the like, and are problematic in this respect.
In view of the above, it is apparent that there exists a need in the art for a coated article that is more durable (e.g., scratch resistant) than is pure titanium oxide. In certain example instances, a low contact angle θ may also be desired.